Pneumatic cylinders are used as actuators in a wide variety of applications. At their most basic, they comprise a cylinder tube body having blind (front) and rod (rear) ends and a cylindrical bore travelling from the front to the rear end defining a piston chamber. The blind and rod ends each have inlet-outlet ports for feeding and discharging pressurized air into the bore. A piston assembly seated in the bore is actuated via the inlet-outlet ports, which alternately feed and discharge pressurized air into the bore.
In order to control the speed of the piston at the end of its power stroke and thus limit the wear and tear on the cylinder body, the cylinder is equipped with a cushioning device. In the prior art cylinders, the cushioning device is in the form of a cushion sleeve that is fixed to the cylinder rod. The cushion sleeve sits in a floating cushion seal.
In the first cycle, air is fed into the cylinder through the blind end of the cylinder onto the cushion sleeve and piston assembly. When the pressure has increased to a sufficient level it acts to release the cushion sleeve from the floating cushion seal and the cushion sleeve, piston assembly and cylinder rod are forced down the cylinder bore.
For the return cycle, air is fed into the rod end of the cylinder and vented from the blind end of the cylinder. The pressurized air forces the cylinder rod, piston assembly and cushion sleeve back towards the blind end. At the blind end of the cylinder, the cushion sleeve enters a floating cushion seal that traps air between the blind end of the cylinder and the piston assembly.
While the prior art cushioning sleeve does provide a cushioning effect, it does suffer from several deficiencies. For example, if an exact seal is not made as the cushion sleeve enters the floating cushion seal, the piston assembly will hit the blind end of the cylinder. Furthermore, as the floating cushion seal begins to break down it becomes more difficult to get an exact seal, with the natural result being that the piston assembly hits the blind end of the cylinder more often, eventually causing the cylinder to break. In addition, this type of cushion system creates cylinder bounce. Also, the response time of the cylinder is limited because of the lag time until there is sufficient pressure to release the cushion sleeve from the floating cushion seal.
There is therefore a continuing need for improvement.